I've been giving the stiff propellers argument some thought. I read a candidate-PhD's paper on quadcopter aerodynamics and although it was about a different (but related) flight characteristic, it did make me think of the stresses on the rotor blades during dynamic flight (transitions from hover to forward flight, changes of direction and altitude...basically any situation where the pilot commands a move from equilibrium). If I am flying at full speed in one direction, then slam the stick in the opposite direction, which components of the aircraft take the punishment? The rotor blades take a lot of it...the change in pitch of the rotor plane will cause them to bend (gyroscopic effects), precession effects, and a violent change in loading. I think the blades absorb a lot of those dynamics (through flexing). If very stiff rotor blades are used, I imagine that those same forces (which still exist) get transferred to the motors, the airframe, and specifically the bearings (where the motor casing (the rotor) sits on the stator (the screws that attach the motor mounts to the printed circuit board).
I guess I should get to my point--I think the more flexible OEM blades act as a sort of "shock absorber" and spare the motor mounts from a lot of the stress of dynamic maneuver. I wonder if using stiffer propeller blades won't result in the motor mounts (or airframe) failing sooner due to increased stresses. Has anyone broken an OEM blade simply from a violent maneuver (not from hitting something)?
Obviously, if you "fly it like you stole it" you are going to break something. My "somewhat informed / somewhat intuitive" opinion is this: If you use stiffer propellers hoping to get better performance (longer battery life, "snappier" response) then realize that you may be overstressing other parts of the airframe, *if* you perform high stress maneuvers. If you don't demand the aircraft to perform high stress maneuvers, then you will probably see some performance improvement, without adversely affecting the longevity of the airframe. I don't do high stress maneuvers, so I may consider stiffer propellers in the future.
I'm not the expert, and I don't plan on testing this, but it is my theory and opinion, based on what I've observed and what I know. Good luck!
(Now I need to see if I can find about $4K lying around so I can buy myself an
Inspire 2 package !!)